The invention relates to a control relay for switching coil currents of contactors, starters and other control relays. More particularly, it relates to a relay of the type having a stationary core and a movable armature each having three pole faces that form three substantially parallel legs in a magnetic circuit; one of which is interrupted by a non-magnetic gap, commonly called an airgap.
In the past, it has been common practice in relays of this type to provide some means for preventing a complete closure of the airgap. The prior art reveals various forms of airgap maintenance including projections into the airgap from either the movable armature member or the stationary core member; a stationary stop member engageable by the movable armature or some portion of the mechanism connected to the armature, e.g., U.S. Pat. No. 1,697,953; and a wear resistant non-magnetic surface on the pole faces of the magnetic device, e.g., U.S. Pat. No. 2,239,267 and U.S. Pat. No. 3,573,690.
The airgap is included in a closed magnetic circuit to reduce the level of residual flux and force required to separate the armature and core upon de-energization of the coil.